Journal of Physical Chemistry B, Vol.101, No.33, 6443-6449, 1997
In-Situ Vibrational Study of the Initial Steps During Urea Electrochemical Oxidation
The electrochemical oxidation of urea has been studied by in situ Fourier transform infrared spectroscopy in supporting electrolytes of different pH. It has been found that the adsorbates and reaction products are strongly pH-dependent. In acidic solutions, the urea is adsorbed through the nitrogen atoms. A two-proton loss is proposed for the adsorption process, related to an excess reversible charge at the end of the hydrogen adsorption/desorption. Adsorbed CO is formed as a result of the hydrolysis of the urea molecule close to the platinum electrode. The main product detected has been CO2. For neutral solutions, the urea molecule leads to the formation of CNO- and [N2O2](2-) ions at potentials in the double-layer region of the platinum electrode. At higher potentials, formation of NO2 and NO3- have been detected. In alkaline media the coordination of adsorbed urea depends an the potential. At lower potentials urea is coordinated through a single NH2 group, and at more anodic potentials the adsorbed urea changes to an adsorption through the oxygen atom.